System and method for capturing facial and body motion

ABSTRACT

A system and method for capturing motion comprises a motion capture volume adapted to contain at least one actor having body markers defining plural body points and facial markers defining plural facial points. A plurality of body motion cameras and a plurality of facial motion cameras are arranged around a periphery of the motion capture volume. The facial motion cameras each have a respective field of view narrower than a corresponding field of view of the body motion cameras. The facial motion cameras are arranged such that all laterally exposed surfaces of the actor while in motion within the motion capture volume are within the field of view of at least one of the plurality of facial motion cameras at substantially all times. A motion capture processor is coupled to the plurality of facial motion cameras and the plurality of body motion cameras to produce a digital model reflecting combined body and facial motion of the actor. At least one microphone may be oriented to pick up audio from the motion capture volume.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority pursuant to 35 U.S.C. § 119(e) to U.S.provisional patent application Ser. No. 60/454,872, filed Mar. 13, 2003,entitled “Motion Capture System.”

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to three-dimensional graphics andanimation, and more particularly, to a motion capture system thatenables both facial and body motion to be captured simultaneously withina volume that can accommodate plural actors.

2. Description of Related Art

Motion capture systems are used to capture the movement of a real objectand map it onto a computer generated object. Such systems are often usedin the production of motion pictures and video games for creating adigital representation of a person that is used as source data to createa computer graphics (CG) animation. In a typical system, an actor wearsa suit having markers attached at various locations (e.g., having smallreflective markers attached to the body and limbs) and digital camerasrecord the movement of the actor from different angles whileilluminating the markers. The system then analyzes the images todetermine the locations (e.g., as spatial coordinates) and orientationof the markers on the actor's suit in each frame. By tracking thelocations of the markers, the system creates a spatial representation ofthe markers over time and builds a digital representation of the actorin motion. The motion is then applied to a digital model, which may thenbe textured and rendered to produce a complete CG representation of theactor and/or performance. This technique has been used by specialeffects companies to produce incredibly realistic animations in manypopular movies.

Motion capture systems are also used to track the motion of facialfeatures of an actor to create a representation of the actor's facialmotion and expression (e.g., laughing, crying, smiling, etc.). As withbody motion capture, markers are attached to the actor's face andcameras record the actor's expressions. Since facial movement involvesrelatively small muscles in comparison to the larger muscles involved inbody movement, the facial markers are typically much smaller than thecorresponding body markers, and the cameras typically have higherresolution than cameras usually used for body motion capture. Thecameras are typically aligned in a common plane with physical movementof the actor restricted to keep the cameras focused on the actor's face.The facial motion capture system may be incorporated into a helmet orother implement that is physically attached to the actor so as touniformly illuminate the facial markers and minimize the degree ofrelative movement between the camera and face. For this reason, facialmotion and body motion are usually captured in separate steps. Thecaptured facial motion data is then combined with captured body motiondata later as part of the subsequent animation process.

An advantage of motion capture systems over traditional animationtechniques, such as keyframing, is the capability of real-timevisualization. The production team can review the spatial representationof the actor's motion in real-time or near real-time, enabling the actorto alter the physical performance in order to capture optimal data.Moreover, motion capture systems detect subtle nuances of physicalmovement that cannot be easily reproduced using other animationtechniques, thereby yielding data that more accurately reflects naturalmovement. As a result, animation created using source material that wascollected using a motion capture system will exhibit a more lifelikeappearance.

Notwithstanding these advantages of motion capture systems, the separatecapture of facial and body motion often results in animation data thatis not truly lifelike. Facial motion and body motion are inextricablylinked, such that a facial expression is often enhanced by correspondingbody motion. For example, an actor may utilize certain body motion(i.e., body language) to communicate emotions and emphasizecorresponding facial expressions, such as using arm flapping whentalking excitedly or shoulder shrugging when frowning. This linkagebetween facial motion and body motion is lost when the motions arecaptured separately, and it is difficult to synchronize these separatelycaptured motions together. When the facial motion and body motion arecombined, the resulting animation will often appear noticeably abnormal.Since it is an objective of motion capture to enable the creation ofincreasingly realistic animation, the decoupling of facial and bodymotion represents a significant deficiency of conventional motioncapture systems.

Another drawback of conventional motion capture systems is that motiondata of an actor may be occluded by interference with other objects,such as props or other actors. Specifically, if a portion of the body orfacial markers is blocked from the field of view of the digital cameras,then data concerning that body or facial portion is not collected. Thisresults in an occlusion or hole in the motion data. While the occlusioncan be filled in later during post-production using conventionalcomputer graphics techniques, the fill data lacks the quality of theactual motion data, resulting in a defect of the animation that may bediscernable to the viewing audience. To avoid this problem, conventionalmotion capture systems limit the number of objects that can be capturedat one time, e.g., to a single actor. This also tends to make the motiondata appear less realistic, since the quality of an actor's performanceoften depends upon interaction with other actors and objects. Moreover,it is difficult to combine these separate performances together in amanner that appears natural.

Yet another drawback of conventional motion capture systems is thataudio is not recorded simultaneously with the motion capture. Inanimation, it is common to record the audio track first, and thenanimate the character to match the audio track. During facial motioncapture, the actor will lip synch to the recorded audio track. Thisinevitably results in a further reduction of the visual quality of themotion data, since it is difficult for an actor to perfectly synchronizefacial motion to the audio track. Also, body motion often affects theway in which speech is delivered, and the separate capture of body andfacial motion increases the difficulty of synchronizing the audio trackto produce a cohesive end product.

Accordingly, it would be desirable to provide a motion capture systemthat overcomes these and other drawbacks of the prior art. Morespecifically, it would be desirable to provide a motion capture systemthat enables both body and facial motion to be captured simultaneouslywithin a volume that can accommodate plural actors. It would also bedesirable to provide a motion capture system that enables audiorecording simultaneously with body and facial motion capture.

SUMMARY OF THE INVENTION

In accordance with the teachings of the present invention, a motioncapture system and method is provided that enables both facial and bodymotion to be captured simultaneously within a volume that canaccommodate plural actors. The motion capture system and method alsoenables audio recording simultaneously with body and facial motioncapture.

More particularly, a system and method for capturing motion comprises amotion capture volume adapted to contain at least one actor having bodymarkers defining plural body points and facial markers defining pluralfacial points. The motion capture volume may have any desired geometricshape, such as oval, round, rectangular, polygonal, etc. A plurality ofbody motion cameras and a plurality of facial motion cameras arearranged around a periphery of the motion capture volume. The facialmotion cameras each have a respective field of view narrower than acorresponding field of view of the body motion cameras. The facialmotion cameras are arranged such that all laterally exposed surfaces ofthe actor while in motion within the motion capture volume are withinthe field of view of at least one of the plurality of facial motioncameras at substantially all times. A motion capture processor iscoupled to the plurality of facial motion cameras and the plurality ofbody motion cameras to produce a digital model reflecting combined bodyand facial motion of the actor. At least one microphone may be orientedto pick up audio from the motion capture volume.

In an embodiment of the invention, the motion capture volume furthercomprises a rectangular area subdivided into a plurality of quadrants.The quadrants each further comprise plural edges coincident with theperiphery of the motion capture volume. The plurality of facial motioncameras further include first subgroups of cameras oriented towardrespective ones of the edges. The plurality of facial motion cameras mayfurther include second subgroups of cameras oriented toward respectiveones of the edges and spatially separated from the first subgroups ofcameras. The first subgroups of cameras are oriented with respect to thesecond subgroups of cameras so that their respective fields of viewsubstantially overlap. The first and second subgroups of cameras mayeach further comprise at least three cameras. The plurality of facialmotion cameras may further comprise third subgroups of cameras disposedrespectively at corners of the motion capture volume and orientedgenerally toward a center of the motion capture volume.

In another embodiment of the invention, at least a first portion of theplurality of facial motion cameras are disposed at a first height aboveground, and at least a second portion of the plurality of facial motioncameras are disposed at a second height above ground that is greaterthan the first height. The first portion of the plurality of facialmotion cameras may be oriented slightly upward to not encompass withintheir respective fields of view other ones of the first portion of theplurality of facial motion cameras disposed substantially across themotion capture volume.

In yet another embodiment of the invention, the plurality of facialmotion cameras and the plurality of body motion cameras each furthercomprise a polarized light source oriented to illuminate the motioncapture volume and a polarized filter to block polarized light from likelight sources of other cameras disposed across the motion capturevolume.

A more complete understanding of the system and method for capturingbody and facial motion will be afforded to those skilled in the art, aswell as a realization of additional advantages and objects thereof, by aconsideration of the following detailed description of the preferredembodiment. Reference will be made to the appended sheets of drawingswhich will first be described briefly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a motion capture system inaccordance with an embodiment of the present invention;

FIG. 2 is a top view of a motion capture volume with a plurality ofmotion capture cameras arranged around the periphery of the motioncapture volume;

FIG. 3 is a side view of the motion capture volume with a plurality ofmotion capture cameras arranged around the periphery of the motioncapture volume;

FIG. 4 is a top view of the motion capture volume illustrating anexemplary arrangement of facial motion cameras with respect to aquadrant of the motion capture volume;

FIG. 5 is a top view of the motion capture volume illustrating anexemplary arrangement of facial motion cameras with respect to cornersof the motion capture volume;

FIG. 6 is a perspective view of the motion capture volume illustrating amotion capture data reflecting two actors in the motion capture volume;

FIG. 7 illustrates motion capture data reflecting two actors in themotion capture volume and showing occlusions regions of the data;

FIG. 8 illustrates motion capture data as in FIG. 7, in which one of thetwo actors has been obscured by an occlusion region; and

FIG. 9 is a block diagram illustrating an alternative embodiment of themotion capture cameras utilized in the motion capture system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As will be further described below, the present invention satisfies theneed for a motion capture system that enables both body and facialmotion to be captured simultaneously within a volume that canaccommodate plural actors. Further, the present invention also satisfiesthe need for a motion capture system that enables audio recordingsimultaneously with body and facial motion capture. In the detaileddescription that follows, like element numerals are used to describelike elements illustrated in one or more of the drawings.

Referring first to FIG. 1, a block diagram illustrates a motion capturesystem 10 in accordance with an embodiment of the present invention. Themotion capture system 10 includes a motion capture processor 12 adaptedto communicate with a plurality of facial motion cameras 14 ₁–14 _(N)and a plurality of body motion cameras 16 ₁–16 _(N). The motion captureprocessor 12 may further comprise a programmable computer having a datastorage device 20 adapted to enable the storage of associated datafiles. One or more computer workstations 18 ₁–18 _(N) may be coupled tothe motion capture processor 12 using a network to enable multiplegraphic artists to work with the stored data files in the process ofcreating a computer graphics animation. The facial motion cameras 14₁–14 _(N) and body motion cameras 16 ₁–16 _(N) are arranged with respectto a motion capture volume (described below) to capture the combinedmotion of one or more actors performing within the motion capturevolume.

Each actor's face and body is marked with markers that are detected bythe facial motion cameras 14 ₁–14 _(N) and body motion cameras 16 ₁–16_(N) during the actor's performance within the motion capture volume.The markers may be reflective or illuminated elements. Specifically,each actor's body may be marked with a plurality of reflective markersdisposed at various body locations including head, legs, arms, andtorso. The actor may be wearing a body suit formed of non-reflectivematerial to which the markers are attached. The actor's face will alsobe marked with a plurality of markers. The facial markers are generallysmaller than the body markers and a larger number of facial markers areused than body markers. To capture facial motion with sufficientresolution, it is anticipated that a high number of facial markers beutilized (e.g., more than 100). In one exemplary implementation, 152small facial markers and 64 larger body markers are affixed to theactor. The body markers may have a width or diameter in the range of 5to 9 millimeters, while the face markers may have a width or diameter inthe range of 2 to 4 millimeters.

To ensure consistency of the placement of the face markers, a mask maybe formed of each actor's face with holes drilled at appropriatelocations corresponding to the desired marker locations. The mask may beplaced over the actor's face, and the hole locations marked directly onthe face using a suitable pen. The facial markers can then be applied tothe actor's face at the marked locations. The facial markers may beaffixed to the actor's face using suitable materials known in thetheatrical field, such as make-up glue. This way, a motion captureproduction that extends over a lengthy period of time (e.g., months) canobtain reasonably consistent motion data for an actor even though themarkers are applied and removed each day.

The motion capture processor 12 processes two-dimensional imagesreceived from the facial motion cameras 14 ₁–14 _(N) and body motioncameras 16 ₁–16 _(N) to produce a three-dimensional digitalrepresentation of the captured motion. Particularly, the motion captureprocessor 12 receives the two-dimensional data from each camera andsaves the data in the form of multiple data files into data storagedevice 20 as part of an image capture process. The two-dimensional datafiles are then resolved into a single set of three-dimensionalcoordinates that are linked together in the form of trajectory filesrepresenting movement of individual markers as part of an imageprocessing process. The image processing process uses images from one ormore cameras to determine the location of each marker. For example, amarker may only be visible to a subset of the cameras due to occlusionby facial features or body parts of actors within the motion capturevolume. In that case, the image processing uses the images from othercameras that have an unobstructed view of that marker to determine themarker's location in space.

By using images from multiple cameras to determine the location of amarker, the image processing process evaluates the image informationfrom multiple angles and uses a triangulation process to determine thespatial location. Kinetic calculations are then performed on thetrajectory files to generate the digital representation reflecting bodyand facial motion corresponding to the actors' performance. Using thespatial information over time, the calculations determine the progressof each marker as it moves through space. A suitable data managementprocess may be used to control the storage and retrieval of the largenumber files associated with the entire process to/from the data storagedevice 20. The motion capture processor 12 and workstations 18 ₁–18 _(N)may utilize commercial software packages to perform these and other dataprocessing functions, such as available from Vicon Motion Systems orMotion Analysis Corp.

The motion capture system 10 further includes the capability to recordaudio in addition to motion. A plurality of microphones 24 ₁–24 _(N) maybe arranged around the motion capture volume to pick up audio (e.g.,spoken dialog) during the actors' performance. The motion captureprocessor 12 may be coupled to the microphones 24 ₁–24 _(N), eitherdirectly or though an audio interface 22. The microphones 24 ₁–24 _(N)may be fixed in place, or may be moveable on booms to follow the motion,or may be carried by the actors and communicate wirelessly with themotion capture processor 12 or audio interface 22. The motion captureprocessor 12 would receive and store the recorded audio in the form ofdigital files on the data storage device 20 with a time track or otherdata that enables synchronization with the motion data.

FIGS. 2 and 3 illustrate an exemplary motion capture volume 30surrounded by a plurality of motion capture cameras. The motion capturevolume 30 includes a peripheral edge 32. The motion capture volume 30 isillustrated as a rectangular-shaped region subdivided by grid lines. Itshould be appreciated that the motion capture volume 30 actuallycomprises a three-dimensional space with the grid defining a floor forthe motion capture volume. Motion would be captured within thethree-dimensional space above the floor. In a preferred embodiment ofthe invention, the motion capture volume 30 comprises a floor area ofapproximately 10 feet by 10 feet, with a height of approximately 6 feetabove the floor. Other size and shape motion capture volumes could alsobe advantageously utilized to suit the particular needs of a production,such as oval, round, rectangular, polygonal, etc.

FIG. 2 illustrates a top view of the motion capture volume 30 with theplurality of motion capture cameras arranged around the peripheral edge32 in a generally circular pattern. Individual cameras are representedgraphically as triangles with the acute angle representing the directionof the lens of the camera, so it should be appreciated that theplurality of cameras are directed toward the motion capture volume 30from a plurality of distinct directions. More particularly, theplurality of motion capture cameras further include a plurality of bodymotion cameras 16 ₁–16 ₈ and a plurality of facial motion cameras 14₁–14 _(N). In view of the high number of facial motion cameras in FIG.2, it should be appreciated that many are not labeled. In the presentembodiment of the invention, there are many more facial motion camerasthan body motion cameras. The body motion cameras 16 ₁–16 ₈ are arrangedroughly two per side of the motion capture volume 30, and the facialmotion cameras 14 ₁–14 _(N) are arranged roughly twelve per side of themotion capture volume 30. The facial motion cameras 14 ₁–14 _(N) and thebody motion cameras 16 ₁–16 _(N) are substantially the same except thatthe focusing lenses of the facial motion cameras are selected to providenarrower field of view than that of the body motion cameras.

FIG. 3 illustrates a side view of the motion capture volume 30 with theplurality of motion capture cameras arranged into roughly three tiersabove the floor of the motion capture volume. A lower tier includes aplurality of facial motion cameras 14 ₁–14 ₃₂, arranged roughly eightper side of the motion capture volume 30. In an embodiment of theinvention, each of the lower tier facial motion cameras 14 ₁–14 ₃₂ areaimed slightly upward so as to not include a camera roughly opposite themotion capture volume 30 from being included within the field of view.The motion capture cameras generally include a light source (e.g., anarray of light emitting diodes) used to illuminate the motion capturevolume 30. It is desirable to not have a motion capture camera “see” thelight source of another motion capture camera, since the light sourcewill appear to the motion capture camera as a bright reflectance thatwill overwhelm data from the reflective markers. A middle tier includesa plurality of body motion cameras 16 ₃–16 ₇ arranged roughly two perside of the motion capture volume 30. As discussed above, the bodymotion cameras have a wider field of view than the facial motioncameras, enabling each camera to include a greater amount of the motioncapture volume 30 within its respective field of view.

The upper tier includes a plurality of facial motion cameras (e.g., 14₃₃–14 ₅₂), arranged roughly five per side of the motion capture volume30. In an embodiment of the invention, each of the upper tier facialmotion cameras 14 ₃₃–14 ₅₂ are aimed slightly downward so as to notinclude a camera roughly opposite the motion capture volume 30 frombeing included within the field of view. Shown on the left-hand side ofFIG. 2, a number of facial motion cameras (e.g., 14 ₅₃–14 ₆₀) are alsoincluded in the middle tier focused on the front edge of the motioncapture volume 30. Since the actors' performance will be generallyfacing the front edge of the motion capture volume 30, the number ofcameras in that region are increased to reduce the amount of data lostto occlusion. In addition a number of facial motion cameras (e.g., 14₆₁–14 ₆₄) are included in the middle tier focused on the corners of themotion capture volume 30. These cameras also serve to reduce the amountof data lost to occlusion.

In the preferred embodiment of the invention, the body and facial motioncameras record images of the marked actors from many different angles sothat substantially all of the lateral surfaces of the actors are exposedto at least one camera at all times. More specifically, it is preferredthat the arrangement of cameras provide that substantially all of thelateral surfaces of the actors are exposed to at least three cameras atall times. By placing the cameras at multiple heights, irregularsurfaces can be modeled as the actor moves within the motion capturefield 30. The present motion capture system 10 thereby records theactors' body movement simultaneously with facial movement (i.e.,expressions). As discussed above, audio recording can also be conductedsimultaneously with motion capture.

FIG. 4 is a top view of the motion capture volume 30 illustrating anexemplary arrangement of facial motion cameras. The motion capturevolume 30 is graphically divided into quadrants, labeled a, b, c and d.Facial motion cameras are grouped into clusters 36, 38, with each cameracluster representing a plurality of cameras. For example, one suchcamera cluster may include two facial motion cameras located in thelower tier and one facial motion camera located in the upper tier. Otherarrangements of cameras within a cluster could also be advantageouslyutilized. The two camera clusters 36, 38 are physically disposedadjacent to each other, yet offset horizontally from each other by adiscernable distance. The two camera clusters 36, 38 are each focused onthe front edge of quadrant d from an angle of approximately 45°. Thefirst camera cluster 36 has a field of view that extends from partiallyinto the front edge of quadrant c to the right end of the front edge ofquadrant d. The second camera cluster 38 has a field of view thatextends from the left end of the front edge of quadrant d to partiallyinto the right edge of quadrant d. Thus, the respective fields of viewof the first and second camera clusters 36, 38 overlap over thesubstantial length of the front edge of quadrant d. A similararrangement of camera clusters is included for each of the other outeredges (coincident with peripheral edge 32) of quadrants a, b, c and d.

FIG. 5 is a top view of the motion capture volume 30 illustratinganother exemplary arrangement of facial motion cameras. As in FIG. 4,the motion capture volume 30 is graphically divided into quadrants a, b,c and d. Facial motion cameras are grouped into clusters 42, 44, witheach camera cluster representing a plurality of cameras. As in theembodiment of FIG. 4, the clusters may comprise one or more cameraslocated at various heights. In this arrangement, the camera clusters 42,44 are located at corners of the motion capture volume 30 facing intothe motion capture volume. These corner camera clusters 42, 44 wouldrecord images of the actors that are not picked up by the other cameras,such as due to occlusion. Other like camera clusters would also belocated at the other corners of the motion capture volume 30.

Having a diversity of camera heights and angles with respect to themotion capture volume 30 serves to increase the available data capturedfrom the actors in the motion capture volume and reduces the likelihoodof data occlusion. It also permits a plurality of actors to be motioncaptured simultaneously within the motion capture volume 30. Moreover,the high number and diversity of the cameras enables the motion capturevolume 30 to be substantially larger than that of the prior art, therebyenabling a greater range of motion within the motion capture volume andhence more complex performances. It should be appreciated that numerousalternative arrangements of the body and facial motion cameras can alsobe advantageously utilized. For example, a greater or lesser number ofseparate tiers could be utilized, and the actual height of each camerawithin an individual tier could be varied.

In the foregoing description of the preferred embodiment of theinvention, the body and facial motion cameras remain fixed in placed.This way, the motion capture processor 12 has a fixed reference pointagainst which movement of the body and facial markers can be measured. Adrawback of this arrangement is that it limits the size of the motioncapture volume 30. If it was desired to capture the motion of aperformance that requires a greater volume of space (e.g., a scene inwhich characters are running over a larger distance), the performancewould have to be divided up into a plurality of segments that are motioncaptured separately. In an alternative embodiment of the invention, aportion of the cameras would remain fixed while others would be moved tofollow the action. The moveable cameras could all be movable usingcomputer controlled servomotors or could be moved manually by humancamera operators. The motion capture processor 12 would track themovement of the cameras, and remove this movement in the subsequentprocessing of the captured data to generate the three-dimensionaldigital representation reflecting body and facial motion correspondingto the actors' performances.

FIG. 6 is a perspective view of the motion capture volume 30illustrating motion capture data reflecting two actors 52, 54 within themotion capture volume. The view of FIG. 6 reflects how the motioncapture data would be viewed by an operator of a workstation 18 asdescribed above with respect to FIG. 1. Similar to FIGS. 2 and 3(above), FIG. 6 further illustrates a plurality of facial motioncameras, including cameras 14 ₁–14 ₁₂ located in a lower tier, cameras14 ₃₃–14 ₄₀ located in an upper tier, and cameras 14 ₆₀, 14 ₆₂ locatedin the corners of motion capture volume 30. The two actors 52, 54 appearas a cloud of dots corresponding to the reflective markers on their bodyand face. As shown and discussed above, there are a much higher numberof markers located on the actors' faces than on their bodies. Themovement of the actors' bodies and faces is tracked by the motioncapture system 10, as substantially described above.

Referring now to FIGS. 7 and 8, motion capture data is shown as it wouldbe viewed by an operator of a workstation 18. As in FIG. 6, the motioncapture data reflects two actors 52, 54 in which the high concentrationof dots reflects the actors' faces and the other dots reflect bodypoints. The motion capture data further includes three occlusion regions62, 64, 66 illustrated as oval shapes. The occlusion regions 62, 64, 66represent places in which reliable motion data was not captured due tolight from one of the cameras falling within the fields of view of othercameras. This light overwhelms the illumination from the reflectivemarkers, and is interpreted by motion capture processor 12 as a body orfacial marker. The image processing process executed by the motioncapture processor 12 generates a virtual mask that filters out thecamera illumination by defining the occlusion regions 62, 64, 66illustrated in FIGS. 7 and 8. The production company can attempt tocontrol the performance of the actors to physically avoid movement thatis obscured by the occlusion regions. Nevertheless, some loss of datacapture inevitably occurs, as shown in FIG. 8 in which the face of actor54 has been almost completely obscured by physical movement into theocclusion region 64.

FIG. 9 illustrates an embodiment of the motion capture system thatreduces the occlusion problem. Particularly, FIG. 9 illustrates cameras84 and 74 that are physically disposed opposite one another across themotion capture volume (not shown). The cameras 84, 74 include respectivelight sources 88, 78 adapted to illuminate the fields of view of thecameras. The cameras 84, 74 are further provided with polarized filters86, 76 disposed in front of the camera lenses. As will be clear from thefollowing description, the polarized filters 86, 76 are arranged (i.e.,rotated) out of phase with respect to each other. Light source 88 emitslight that is polarized by polarized filter 86. The polarized lightreaches polarized filter 76 of camera 74, but, rather than passingthrough to camera 74, the polarized light is reflected off of orabsorbed by polarized filter 76. As a result, the camera 84 will not“see” the illumination from camera 74, thereby avoiding formation of anocclusion region and obviating the need for virtual masking.

While the preceding description referred to the use of optical sensingof physical markers affixed to the body and face to track motion, itshould be appreciated to those skilled in the art that alternative waysto track motion could also be advantageously utilized. For example,instead of affixing markers, physical features of the actors (e.g.,shapes of nose or eyes) could be used as natural markers to trackmotion. Such a feature-based motion capture system would eliminate thetask of affixing markers to the actors prior to each performance. Inaddition, alternative media other than optical could be used to detectcorresponding markers. For example, the markers could compriseultrasonic or electromagnetic emitters that are detected bycorresponding receivers arranged around the motion capture volume. Inthis regard, it should be appreciated that the cameras described aboveare merely optical sensors and that other types of sensors could also beadvantageously utilized.

Having thus described a preferred embodiment of a system and method forcapturing body and facial motion, it should be apparent to those skilledin the art that certain advantages of the invention have been achieved.It should also be appreciated that various modifications, adaptations,and alternative embodiments thereof may be made within the scope andspirit of the present invention. The invention is further defined by thefollowing claims.

1. A system for capturing combined facial and body motion, comprising: amotion capture volume adapted to contain at least one actor having bodymarkers defining plural body points and facial markers defining pluralfacial points; a plurality of body motion cameras arranged around aperiphery of said motion capture volume; a plurality of facial motioncameras arranged around said periphery of said motion capture volume,said facial motion cameras each having a respective field of viewnarrower than a corresponding field of view of said body motion cameras;said facial motion cameras being arranged such that all laterallyexposed surfaces of said at least one actor while in motion within saidmotion capture volume are within said field of view of at least one ofsaid plurality of facial motion cameras at substantially all times; anda motion capture processor coupled to said plurality of body motioncameras and said plurality of facial motion cameras to simultaneouslyreceive motion capture data from said plurality of body motion camerasand said plurality of facial motion cameras, and produce a digitalrepresentation reflecting combined facial and body motion of said atleast one actor.
 2. The system for capturing motion of claim 1, whereinsaid plurality of facial motion cameras and said plurality of bodymotion cameras are fixed.
 3. The system for capturing motion of claim 1,wherein a portion of said plurality of facial motion cameras and aportion of said plurality of body motion cameras are movable to trackmotion within said motion capture volume.
 4. The system for capturingmotion of claim 1, wherein said plurality of facial motion cameras andsaid plurality of body motion cameras each further comprise polarizedlight sources oriented to illuminate said motion capture volume andpolarized filter to block polarized light from other cameras disposedacross said motion capture volume.
 5. A method for capturing motion,comprising: defining a motion capture volume adapted to contain at leastone actor having body markers defining plural body points and facialmarkers defining plural facial points; arranging a plurality of bodymotion cameras around a periphery of said motion capture volume;arranging a plurality of facial motion cameras around said periphery ofsaid motion capture volume, said facial motion cameras each having arespective field of view narrower than a corresponding field of view ofsaid body motion cameras, said facial motion cameras being arranged suchthat all laterally exposed surfaces of said at least one actor while inmotion within said motion capture volume are within said field of viewof at least one of said plurality of facial motion cameras atsubstantially all times; and simultaneously receiving motion capturedata from said plurality of facial motion cameras and said plurality ofbody motion cameras and producing a digital representation reflectingcombined body and facial motion of said at least one actor.
 6. Themethod for capturing motion of claim 5, further comprising subdividingsaid motion capture volume into a plurality of quadrants, said pluralityof quadrants each further comprising plural edges coincident with saidperiphery of said motion capture volume, and orienting first subgroupsof said plurality of facial motion cameras toward respective ones ofsaid edges.
 7. The method for capturing motion of claim 6, furthercomprising orienting second subgroups of said plurality of facial motioncameras toward respective ones of said edges and spatially separatedfrom said first subgroups of cameras.
 8. The method for capturing motionof claim 7, further comprising orienting said first subgroups of cameraswith respect to said second subgroups of cameras so that theirrespective fields of view substantially overlap.
 9. The method forcapturing motion of claim 7, wherein said first subgroups of cameras andsaid second subgroups of cameras each further comprise at least threecameras.
 10. The method for capturing motion of claim 5, furthercomprising locating third subgroups of said plurality of facial motioncameras at respective corners of said motion capture volume and orientedgenerally toward a center of said motion capture volume.
 11. The methodfor capturing motion of claim 5, further comprising disposing at least afirst portion of said plurality of facial motion cameras at a firstheight above ground, and disposing at least a second portion of saidplurality of facial motion cameras at a second height above groundgreater than said first height.
 12. The method for capturing motion ofclaim 11, further comprising orienting said first portion of saidplurality of facial motion cameras slightly upward to not encompasswithin respective fields of view other ones of said first portion ofsaid plurality of facial motion cameras disposed substantially acrosssaid motion capture volume.
 13. The method for capturing motion of claim5, further comprising fixing in place said plurality of facial motioncameras and said plurality of body motion cameras.
 14. The method forcapturing motion of claim 5, further comprising moving at least aportion of said plurality of facial motion cameras and at least aportion of said plurality of body motion cameras to track motion withinsaid motion capture volume.
 15. The method for capturing motion of claim5, further comprising illuminating said motion capture volume withpolarized light and providing at least a portion of said plurality offacial motion cameras and at least a portion of said plurality of bodymotion cameras with polarization filters to block said polarized lightfrom other ones of said cameras disposed substantially across saidmotion capture volume.
 16. The method for capturing motion of claim 5,further comprising recording audio from within said motion capturevolume.